The term “flame resistant” is used to describe a material that burns slowly or that is self-extinguishing after removal of an external source of ignition. A fabric or yarn may be flame resistant because of the innate properties of the fiber, the twist level of the yarn, the fabric construction, or, as will be discussed herein, the presence of flame retardant chemicals applied to the fabric. The term “flame retardant” or “flame retardant chemical” refers to a chemical compound that may be applied as a topical treatment to a fiber, fabric, or other textile item during processing to reduce its flammability.
Flame resistant fabrics are useful in a number of areas, including the production of garments worn by workers in a variety of industries, including the military, electrical (for arc protection), petroleum chemical manufacturing, and emergency response. Because imparting flame resistance to cellulosic fabrics is relatively routine, the fabrics used in these applications typically have a high cellulosic content (often, 70% or more). Unfortunately, fabrics with such high cellulosic content tend to exhibit deficiencies in terms of durability, abrasion resistance, and drying time that make them unsuitable for a number of applications, including, for example, uniform and protective garments. For these reasons, manufacturers have long sought ways of incorporating higher percentages of synthetic fibers into these fabrics. The difficulty with accommodating this desire is the tendency of the synthetic fibers to burn or melt and the tendency of the hydrophobic synthetic fibers to resist penetration of the flame retardant, thereby making them unsuitable for use in large percentages.
Until now, to achieve flame resistant properties in cellulosic-containing fabrics, the fabrics have been subjected to an “ammonia process,” in which the target fabric is dipped in a bath containing a phosphorous-based flame retardant chemical, dried at relatively low temperatures, conveyed through a chamber containing gaseous ammonia, and then dipped in separate baths of peroxide and caustic before drying. One obvious disadvantage of this process is the high capital investment associated with installing an ammonia chamber and requisite environmental controls, as well as the expenses associated with its operation and maintenance. Although fabrics produced by the ammonia process possess a soft hand and good tear strength, they tend to have poor wrinkle resistance and appearance retention. In addition, the method in which they are produced limits the ability to apply additional finishing agents (e.g., soil repel agents, stain release agents, permanent press resins, and the like) due to the tendency of malodors to be generated when the fabrics are heat-set at high temperatures. Finally, because the ammonia process tends to preferentially bind the flame retardant chemical to the cellulosic fibers in the fabric, the amount of synthetic fiber content has heretofore been limited to less than 30%.
An alternate approach, which was considered but not widely accepted for commercial use, involves padding a phosphorous-based flame retardant chemical onto a target fabric and then curing the treated fabric at high temperatures. This process results in fabric with low tear strength, due to the flame retardant chemical interacting too vigorously with the cellulosic fibers, and with a stiff hand. These characteristics render the fabrics produced using this process unsuitable for use as apparel fabrics.
The present process overcomes the shortcomings of the previous approaches by providing an alternative mechanism by which one or more flame retardant chemicals may be fixed on a target textile substrate. As a result, the fabrics exhibit a durable finish, and larger amounts of synthetic fibers may successfully be incorporated into the fabrics without a loss of flame resistance. These larger amounts of synthetic fibers contribute significantly to increasing the durability and the tear strength of the treated fabrics.